Nano- and Microcomposites for Electrical Engineering Applications Frank Wiesbrock www.mdpi.com/journal/polymers Edited by polymers Printed Edition of the Special Issue Published in Polymers Frank Wiesbrock (Ed.) Nano- and Microcomposites for Electrical Engineering Applications This book is a reprint of the Special Issue that appeared in the online, open access journal, Polymers (ISSN 2073-4360) in 2016, available at: http://www.mdpi.com/journal/polymers/special_issues/nano_microcomposites Guest Editor Frank Wiesbrock PCCL—Polymer Competence Center Leoben GmbH Austria Editorial Office MDPI AG St. Alban-Anlage 66 Basel, Switzerland Publisher Shu-Kun Lin Assistant Managing Editor Lynn Huang Assistant Editor Tian Li 1. Edition 2016 MDPI • Basel • Beijing • Wuhan • Barcelona • Belgrade ISBN 978-3-03842-292-1 (Hbk) ISBN 978-3-03842-293-8 (electronic) Articles in this volume are Open Access and distributed under the Creative Commons Attribution license (CC BY), which allows users to download, copy and build upon published articles even for commercial purposes, as long as the author and publisher are properly credited, which ensures maximum dissemination and a wider impact of our publications. The book taken as a whole is © 2016 MDPI, Basel, Switzerland, distributed under the terms and conditions of the Creative Commons by Attribution (CC BY-NC-ND) license (http://creativecommons.org/licenses/by-nc-nd/4.0/). III Table of Contents List of Contributors ......................................................................................................... VII About the Guest Editor..................................................................................................... XI Frank Wiesbrock Preface to “Interdisciplinary Approaches towards Materials with Enhanced Properties for Electrical Engineering” Reprinted from: Polymers 2016 , 8 (8), 307 http://www.mdpi.com/2073-4360/8/8/307................................................................... XIII Ilona Pleşa, Petru V. Noţingher, Sandra Schlögl, Christof Sumereder and Michael Muhr Properties of Polymer Composites Used in High-Voltage Applications Reprinted from: Polymers 2016 , 8 (5), 173 http://www.mdpi.com/2073-4360/8/5/173........................................................................ 1 Andreas Moser and Michael Feuchter Mechanical Properties of Composites Used in High-Voltage Applications Reprinted from: Polymers 2016 , 8 (7), 260 http://www.mdpi.com/2073-4360/8/7/260...................................................................... 92 Natascha Andraschek, Andrea Johanna Wanner, Catharina Ebner and Gisbert Riess Mica/Epoxy-Composites in the Electrical Industry: Applications, Composites for Insulation, and Investigations on Failure Mechanisms for Prospective Optimizations Reprinted from: Polymers 2016 , 8 (5), 201 http://www.mdpi.com/2073-4360/8/5/201.................................................................... 107 Gwang - Seok Song, Dai Soo Lee and Ilho Kang The Effects of in Situ -Formed Silver Nanoparticles on the Electrical Properties of Epoxy Resin Filled with Silver Nanowires Reprinted from: Polymers 2016 , 8 (4), 157 http://www.mdpi.com/2073-4360/8/4/157.................................................................... 138 IV Celia Yeung and Alun S. Vaughan On the Effect of Nanoparticle Surface Chemistry on the Electrical Characteristics of Epoxy-Based Nanocomposites Reprinted from: Polymers 2016 , 8 (4), 126 http://www.mdpi.com/2073-4360/8/4/126.................................................................... 150 Anh T. Hoang, Love Pallon, Dongming Liu, Yuriy V. Serdyuk, Stanislaw M. Gubanski and Ulf W. Gedde Charge Transport in LDPE Nanocomposites Part I—Experimental Approach Reprinted from: Polymers 2016 , 8 (3), 87 http://www.mdpi.com/2073-4360/8/3/87...................................................................... 173 Anh T. Hoang, Yuriy V. Serdyuk and Stanislaw M. Gubanski Charge Transport in LDPE Nanocomposites Part II—Computational Approach Reprinted from: Polymers 2016 , 8 (4), 103 http://www.mdpi.com/2073-4360/8/4/103.................................................................... 199 Martin Fimberger, Ioannis - Alexandros Tsekmes, Roman Kochetov, Johan J. Smit and Frank Wiesbrock Crosslinked Poly(2-oxazoline)s as “Green” Materials for Electronic Applications Reprinted from: Polymers 2016 , 8 (1), 6 http://www.mdpi.com/2073-4360/8/1/6........................................................................ 221 Sheng Chen, Rui Ding, Xiuling Ma, Liqun Xue, Xiuzhu Lin, Xiaoping Fan and Zhimin Luo Preparation of Highly Dispersed Reduced Graphene Oxide Modified with Carboxymethyl Chitosan for Highly Sensitive Detection of Trace Cu(II) in Water Reprinted from: Polymers 2016 , 8 (4), 78 http://www.mdpi.com/2073-4360/8/4/78...................................................................... 237 Shaohui Liu, Shaomei Xiu, Bo Shen, Jiwei Zhai and Ling Bing Kong Dielectric Properties and Energy Storage Densities of Poly(vinylidenefluoride) Nanocomposite with Surface Hydroxylated Cube Shaped Ba 0.6Sr 0.4 TiO 3 Nanoparticles Reprinted from: Polymers 2016 , 8 (2), 45 http://www.mdpi.com/2073-4360/8/2/45...................................................................... 253 V Valentina Allodi, Sergio Brutti, Marco Giarola, Mirko Sgambetterra, Maria Assunta Navarra, Stefania Panero and Gino Mariotto Structural and Spectroscopic Characterization of A Nanosized Sulfated TiO 2 Filler and of Nanocomposite Nafion Membranes Reprinted from: Polymers 2016 , 8 (3), 68 http://www.mdpi.com/2073-4360/8/3/68...................................................................... 268 VII List of Contributors Valentina Allodi Department of Computer Science, University of Verona, Strada le Grazie 15, 37134 Verona, Italy. Natascha Andraschek Polymer Competence Center Leoben (PCCL), Roseggerstraße 12, Leoben 8700, Austria. Sergio Brutti Department of Sciences, University of Basilicata, V.le dell’Ateneo Lucano 10, 85100 Potenza, Italy. Sheng Chen School of Ocean Science and Biochemistry Engineering, Fuqing Branch of Fujian Normal University, 1 Longjiang Road, Fuqing 350300, China. Rui Ding College of Environmental Science and Engineering, Fujian Normal University, 8 Shangsan Road, Fuzhou 350007, China. Catharina Ebner Chair of Polymer Chemistry, Montan University Leoben, Otto- Glöckl-Strasse 2, Leoben 8700, Austria. Xiaoping Fan College of Environmental Science and Engineering, Fujian Normal University, 8 Shangsan Road, Fuzhou 350007, China. Michael Feuchter Institute of Material Science and Testing of Polymers, Montanuniversitaet Leoben, 8700 Leoben, Austria; Polymer Competence Center Leoben, 8700 Leoben, Austria. Mar tin Fimberger Polymer Competence Center Leoben, Rosseggerstrasse 12, Leoben 8700, Austria; Institute for Chemistry and Technology of Materials, Graz University of Technology, NAWI Graz, Stremayrgasse 9, Graz 8010, Austria. Ulf W. Gedde Fiber and Polymer Technology, School of Chemical Science and Engineering, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden. Marco Giarola Department of Computer Science, University of Verona, Strada le Grazie 15, 37134 Verona, Italy. Stanislaw M. Gubanski Division of High Voltage Engineering, Department of Materials and Manufacturing Technology, Chalmers University of Technology, Gothenburg SE-41296, Sweden. Anh T. Hoang Division of High Voltage Engineering, Department of Materials and Manufacturing Technology, Chalmers University of Technology, Gothenburg SE-41296, Sweden. Ilho Kang Research Center, NEPES AMC, 99 Seokam-ro, Iksan, Chonbuk 54587, Korea. VIII Roman Kochetov Department of Electrical Sustainable Energy, Delft University of Technology, Mekelweg 4, 2628 CD Delft, The Netherlands; Asea Brown Boveri (ABB) Corporate Research, Segelhofstrasse 1k, 5405 Baden-Daettwil, Switzerland. Ling Bing Kong School of Materials Science and Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore. Dai Soo Lee Division of Semiconductor and Chemical Engineering, Chonbuk National University, Baekjedaero 567, Deokjin-gu, Jeonju, Chonbuk 54896, Korea. Xiuzhu Lin School of Ocean Science and Biochemistry Engineering, Fuqing Branch of Fujian Normal University, 1 Longjiang Road, Fuqing 350300, China. Dongming Liu Fiber and Polymer Technology, School of Chemical Science and Engineering, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden. Shaohui Liu School of Science, Henan Institute of Engineering, Zhengzhou 451191, China; Key Laboratory of Advanced Civil Engineering Materials of Ministry of Education, Functional Materials Research Laboratory, School of Materials Science & Engineering, Tongji University, 4800 Caoan Road, Shanghai 201804, China. Zhimin Luo Jiangsu Key Laboratory for Organic Electronics & Information Displays and Institute of Advanced Materials (IAM), Nanjing University of Posts and Telecommunications, Nanjing 210046, China. Xiuling Ma College of Chemistry and Chemical Engineering, Fujian Normal University, 8 Shangsan Road, Fuzhou 350007, China. Gino Mariotto Department of Computer Science, University of Verona, Strada le Grazie 15, 37134 Verona, Italy. Andreas Moser Institute of Material Science and Testing of Polymers, Montanuniversitaet Leoben, 8700 Leoben, Austria. Michael Muhr Institute of High Voltage Engineering and System Performance, Graz University of Technology, Inffeldgasse 18/I, Graz 8010, Austria. Maria Assunta Navarra Department of Chemistry, Sapienza University of Rome. P.le Aldo Moro 5, 00185 Rome, Italy. Petru V. Noţingher Faculty of Electrical Engineering, Electrotechnical Material Laboratory, University Politehnica of Bucharest, Splaiul Independentei 313, Bucharest 060042, Romania. Love Pallon Fiber and Polymer Technology, School of Chemical Science and Engineering, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden. IX Stefania Panero Department of Chemistry, Sapienza University of Rome. P.le Aldo Moro 5, 00185 Rome, Italy. Ilona Pleşa Polymer Competence Center Leoben GmbH (PCCL), Roseggerstrasse 12, Leoben 8700, Austria. Gisbert Riess Chair of Polymer Chemistry, Montan University Leoben, Otto-Glöckl-Strasse 2, Leoben 8700, Austria. Sandra Schlögl Polymer Competence Center Leoben GmbH (PCCL), Roseggerstrasse 12, Leoben 8700, Austria. Yuriy V. Serdyuk Division of High Voltage Engineering, Department of Materials and Manufacturing Technology, Chalmers University of Technology, Gothenburg SE-41296, Sweden;Division of High Voltage Engineering, Department of Materials and Manufacturing Technology, Chalmers University of Technology, Gothenburg SE-412 96, Sweden. Mirko Sgambetterra Department of Chemistry, Sapienza University of Rome. P.le Aldo Moro 5, 00185 Rome, Italy. Bo Shen Key Laboratory of Advanced Civil Engineering Materials of Ministry of Education, Functional Materials Research Laboratory, School of Materials Science & Engineering, Tongji University, 4800 Caoan Road, Shanghai 201804, China. Johan J. Smit Department of Electrical Sustainable Energy, Delft University of Technology, Mekelweg 4, 2628 CD Delft, The Netherlands. Gwang - Seok Song Division of Semiconductor and Chemical Engineering, Chonbuk National University, Baekjedaero 567, Deokjin-gu, Jeonju, Chonbuk 54896, Korea. Christof Sumerede r Institute of Energy, Transport and Environmental Management, University of Applied Science–FH Joanneum, Werk-VI-Straße 46, Kapfenberg 8605, Austria. Ioannis- Alexandros Tsekmes Department of Electrical Sustainable Energy, Delft University of Technology, Mekelweg 4, 2628 CD Delft, The Netherlands. Alun S. Vaughan Department of Electronics and Computer Science, University of Southampton, Southampton SO17 1BJ, UK. Andrea Johanna Wanner Polymer Competence Center Leoben (PCCL), Roseggerstraße 12, Leoben 8700, Austria. Frank Wiesbrock Polymer Competence Center Leoben, Rosseggerstrasse 12, Leoben 8700, Austria. X Shaomei Xiu Key Laboratory of Advanced Civil Engineering Materials of Ministry of Education, Functional Materials Research Laboratory, School of Materials Science & Engineering, Tongji University, 4800 Caoan Road, Shanghai 201804, China. Liqun Xue School of Ocean Science and Biochemistry Engineering, Fuqing Branch of Fujian Normal University, 1 Longjiang Road, Fuqing 350300, China. Celia Yeung Department of Electronics and Computer Science, University of Southampton, Southampton SO17 1BJ, UK. Jiwei Zhai Key Laboratory of Advanced Civil Engineering Materials of Ministry of Education, Functional Materials Research Laboratory, School of Materials Science & Engineering, Tongji University, 4800 Caoan Road, Shanghai 201804, China. XI About the Guest Edito r Frank Wiesbrock received his doctorate at the Technical University of Munich, Germany, in 2003 for his work on metal ß-amino carboxylates under the supervision of H. Schmidbaur. His subsequent biannual postdoctoral stay with U.S. Schubert at the Eindhoven Technical University focused on block copoly(2-oxazoline)s from microwave-assisted synthesis. He worked as a project manager at Chemspeed Technologies AG in Augst, Switzerland, and returned to academia in 2007 as a Marie Curie ToK researcher with T. Calogeropoulou at the National Hellenic Research Foundation in Athens, Greece. Since 2008, he has been an assistant professor/lecturer at the Graz University of Technology, Austria, where he completed his Habilitation in 2012. Currently he is employed as a senior researcher at the Polymer Competence Center Leoben (PCCL), Austria. His research interests comprise microwave-assisted polymerizations, poly(2-oxazoline)s, biopolymers and biocompatible polymers, and nanocomposites for electronic applications. Preface to ”Interdisciplinary Approaches towards Materials with Enhanced Properties for Electrical Engineering” Frank Wiesbrock Reprinted from Polymers . Cite as: Wiesbrock, F. Interdisciplinary Approaches towards Materials with Enhanced Properties for Electrical Engineering. Polymers 2016 , 8 , 307. The internationally growing demand for electrical energy is one of the most prominent triggers stimulating research these days. In this highly interdisciplinary research area , electrical engineers, material scientists and chemists collaborate for the design and fabrication of the next generation of high-voltage machinery and electro-technical devices. Nanocomposites with enhanced thermal conductivity and improved electric properties are in the center of these joint research activities. Hence, in this Special Issue of the open-access journal Polymers , the state-of-the-art research and technology of the area ‘ micro- and nanocomposites for electrical engineering applications ’ has been summarized in three review articles, while the current research trends and the development and characterization of novel materials have been described in eight original research articles. State-of-the-art of research and technology. The comprehensive review article by Plesa et al. addresses with dedication the structure-property relationships of composite materials with special respect to their electric properties and the resulting potential application fields [ 1 ]. Originating from the high demands regarding the reliability and lifetime expectance of high-voltage engineering machineries such as generators and transformers, the mechanical properties of insulating resins and the corresponding micro- and nanocomposites are of prime importance; this topic has been summarized in the review article by Moser and Feuchter [ 2 ], in which epoxy-based resins are discussed in detail. Mica/epoxy composites are the most commonly used insulation materials in high-voltage rotating machines , and their properties as well as the possibly occurring failure mechanisms of the composite material have been described in the review article by Andraschek and colleagues [3]. Novel composites based on epoxy resins or on low-density polyethylene. The preparation as well as the isotropic electrical properties (in the case of additionally present silver nanowires) of epoxy-based nanocomposites containing in-situ formed silver nanoparticles was reported by Kang, Lee, and Song [ 4 ]. Vaughan and Yeung described the effect of siloxane-mediated surface functionalization of silica nanoparticles [ 5 ]; the corresponding epoxy-based nanocomposites exhibited breakdown strengths that were increased by approx. 50% compared to the unfilled XIII epoxy resin. Gubanski et al. reported the decrease of the direct current conductivity of low-density polyethylene composites containing inorganic fillers such as magnesium oxide and aluminum oxide [ 6 ]. In a subsequent study [ 7 ], a bipolar charge transport model was employed to investigate this reduction, from which the reduced charge injection at electrodes was identified as the most important parameter causing the observed effects. Materials based on polymers from renewable resources and composites based on (per-) fluorinated polymers. Smit, Wiesbrock et al. reported the synthesis of crosslinkable copoly(2-oxazoline)s from fatty acids such as castor oil and coconut oil [ 8 ]. The crosslinked copolymers exhibited electric properties similar to those of polyamides , which renders them medium insulators. The in-situ preparation of reduced graphene oxide/carboxymethyl chitosan composites was described by Luo, Chen, and colleagues [ 9 ]. An electrode modified with this composite showed a high detection performance for bivalent copper ions Nanocomposites of poly (vinylidene fluoride) and cube-shaped surface-hydroxylated Ba 0.6 Sr 0.4 TiO 3 nanoparticles were reported by Zhai et al. to show an increased dielectric constant and improved breakdown strength compared to the unfilled polymer [ 10 ]. Mariotto and colleagues described composites of Nafion and nano-sized sulfated titanium dioxide [ 11 ], in which they found that the inclusion of 2 wt % of fillers yielded structures that consisted of filler-rich regions, which were separated by areas of almost pure Nafion . This structural arrangement does not easily provide any proton percolation path , and, hence, a higher resistance was expected for this composite. In summary, this Special Issue of Polymers compiles the current state-of-the-art of research and technology in the area of ‘ micro- and nanocomposites for electrical engineering applications ’ and highlights prominent current research directions in the field. We very much hope that you enjoy reading it. Acknowledgments: This work was performed in the K-Project PolyComp at the Polymer Competence Center Leoben GmbH within the framework of the COMET-program (Competence Centers for Excellent Technologies) of the Federal Ministry for Transport, Innovation and Technology and Federal Ministry for Economy, Family and Youth. Funding is provided by the Austrian Government and the State Government of Styria. Author Contributions: Frank Wiesbrock wrote the editorial. Conflicts of Interest: The author declares no conflict of interest. References 1. Ple ̧ sa, I.; No ̧ tingher, P.V.; Schlögl, S.; Sumereder, C.; Muhr, M. Properties of Polymer Composites Used in High-Voltage Applications. Polymers 2016 , 8 , 173. 2. Moser, A.; Feuchter, M. Mechanical Properties of Composites Used in High-Voltage Applications. Polymers 2016 , 8 , 260. XIV 3. Andraschek, N.; Wanner, A.J.; Ebner, C.; Riess, G. Mica/Epoxy-Composites in the Electrical Industry: Applications, Composites for Insulation, and Investigations on Failure Mechanisms for Prospective Optimizations. Polymers 2016 , 8 , 201. 4. Song, G.-S.; Lee, D.S.; Kang, I. The Effects of in Situ-Formed Silver Nanoparticles on the Electrical Properties of Epoxy Resin Filled with Silver Nanowires. Polymers 2016 , 8 , 157. 5. Yeung, C.; Vaughan, A.S. On the Effect of Nanoparticle Surface Chemistry on the Electrical Characteristics of Epoxy-Based Nanocomposites. Polymers 2016 , 8 , 126. 6. Hoang, A.T.; Pallon, L.; Liu, D.; Serdyuk, Y.V.; Gubanski, S.M.; Gedde, U.W. Charge Transport in LDPE Nanocomposites Part I—Experimental Approach. Polymers 2016 , 8 , 87. 7. Hoang, A.T.; Serdyuk, Y.V.; Gubanski, S.M. Charge Transport in LDPE Nanocomposites Part II—Computational Approach. Polymers 2016 , 8 , 103. 8. Fimberger, M.; Tsekmes, I.-A.; Kochetov, R.; Smit, J.J.; Wiesbrock, F. Crosslinked Poly(2-oxazoline)s as “Green” Materials for Electronic Applications. Polymers 2016 , 8 , 6. 9. Chen, S.; Ding, R.; Ma, X.; Xue, L.; Lin, X.; Fan, X.; Luo, Z. Preparation of Highly Dispersed Reduced Graphene Oxide Modified with Carboxymethyl Chitosan for Highly Sensitive Detection of Trace Cu(II) in Water. Polymers 2016 , 8 , 78. 10. Liu, S.; Xiu, S.; Shen, B.; Zhai, J.; Kong, L.B. Dielectric Properties and Energy Storage Densities of Poly(vinylidenefluoride) Nanocomposite with Surface Hydroxylated Cube Shaped Ba 0.6 Sr 0.4 TiO 3 Nanoparticles. Polymers 2016 , 8 , 45. 11. Allodi, V.; Brutti, S.; Giarola, M.; Sgambetterra, M.; Navarra, M.A.; Panero, S.; Mariotto, G. Structural and Spectroscopic Characterization of A Nanosized Sulfated TiO2 Filler and of Nanocomposite Nafion Membranes. Polymers 2016 , 8 , 68. XV Properties of Polymer Composites Used in High-Voltage Applications Ilona Ple ̧ sa, Petru V. No ̧ tingher, Sandra Schlögl, Christof Sumereder and Michael Muhr Abstract: The present review article represents a comprehensive study on polymer micro/nanocomposites that are used in high-voltage applications. Particular focus is on the structure-property relationship of composite materials used in power engineering, by exploiting fundamental theory as well as numerical/analytical models and the influence of material design on electrical, mechanical and thermal properties. In addition to describing the scientific development of micro/nanocomposites electrical features desired in power engineering, the study is mainly focused on the electrical properties of insulating materials, particularly cross-linked polyethylene (XLPE) and epoxy resins, unfilled and filled with different types of filler. Polymer micro/nanocomposites based on XLPE and epoxy resins are usually used as insulating systems for high-voltage applications, such as: cables, generators, motors, cast resin dry-type transformers, etc. Furthermore, this paper includes ample discussions regarding the advantages and disadvantages resulting in the electrical, mechanical and thermal properties by the addition of micro- and nanofillers into the base polymer. The study goals are to determine the impact of filler size, type and distribution of the particles into the polymer matrix on the electrical, mechanical and thermal properties of the polymer micro/nanocomposites compared to the neat polymer and traditionally materials used as insulation systems in high-voltage engineering. Properties such as electrical conductivity, relative permittivity, dielectric losses, partial discharges, erosion resistance, space charge behavior, electric breakdown, tracking and electrical tree resistance, thermal conductivity, tensile strength and modulus, elongation at break of micro- and nanocomposites based on epoxy resin and XLPE are analyzed. Finally, it was concluded that the use of polymer micro/nanocomposites in electrical engineering is very promising and further research work must be accomplished in order to diversify the polymer composites matrices and to improve their properties. Reprinted from Polymers . Cite as: Ple ̧ sa, I.; No ̧ tingher, P.V.; Schlögl, S.; Sumereder, C.; Muhr, M. Properties of Polymer Composites Used in High-Voltage Applications. Polymers 2016 , 8 , 173. 1. Introduction In the last two decades, the design of composite materials comprising either micro-scaled or nano-scaled inorganic particles has gained increased attention in 1 power and high-voltage engineering [ 1 – 8 ]. Particularly, the use of micro- and nanotechnologies offers new approaches towards improved insulation systems that operate at higher temperatures and electrical stress. Along with material performance, basic research and development of “advanced” materials in the field of polymer base composites also pursue energy-efficient and low cost manufacturing routes in order to bring new material concepts into marketable products [1]. Composite materials typically consist of two or more components that comprise significantly different physical and/or chemical properties. Due to the controlled combination of the components, new materials are obtained with distinct properties from the individual components [ 2 ]. If at least one of the components has nanometric dimensions, these materials are termed nanocomposites [ 3 ]. In Reference [ 3 ] a nanocomposite is defined as “a multiphase solid material where one of the phases has one, two or three dimensions of less than 100 nanometers (nm), or structures with repeating distances between the different phases in nanoscale that form the material”. Nanocomposites differ from traditional composites in three major aspects: (i) they contain a small amount of filler (usually less than 10 wt % vs. more than 50 wt % for composites); (ii) the filler size is in the range of nanometers in size (10 ́ 9 m vs. 10 ́ 6 m for composites) and (iii) they have tremendously large specific surface area compared to micro-sized composites [ 4 ]. Thus, nanocomposites are characterized by distinctive advantages including homogenous structure, no fiber rupture, and optical transparency, improved or unchanged processabillity [ 4 ]. Depending on the matrix material, nanocomposites can be classified in three major categories: ceramic matrix nanocomposites, metal matrix nanocomposites and polymer matrix nanocomposites [ 5 ]. In Reference [ 4 ], polymer matrix nanocomposites are considered as “polymers in which a small amount of nanometer size fillers ( ď 10 wt %) is homogeneously dispersed”. Composite materials are typically desired to be employed instead of traditional materials due to their enhanced materials performance involving high strength, toughness, heat resistance, light weight, impermeability against gasses, thermal endurance and stability in the presence of aggressive chemicals, water and hydrocarbons, high resistance to fatigue and corrosion degradation, re-processing recyclability and less leakage of small molecules such as stabilizers, etc. [ 4 ]. In particular, in the field of plastic engineering, composite materials are selected as a function of Young’s modulus versus density or yield strength versus density [ 4 ]. For numerous applications in automotive, aircraft or maritime industry, light-weight materials with increased mechanical strength are preferred to be used. The present review addresses polymer based micro- and nanocomposites that are employed in high-voltage applications and gives an overview of electrical, mechanical and thermal properties of composite materials in dependence on the material structures and compositions. 2 In the power industry, inorganic filler (particularly aluminum nitride (AlN), boron nitride (BN), silicon dioxide or silica (SiO 2 ), aluminum oxide or alumina (Al 2 O 3 ), titanium oxide or titania (TiO 2 ), silicon carbide (SiC) and zinc oxide (ZnO), etc. ) are usually incorporated into electrical insulating polymers to achieve specific electrical, mechanical, and thermal properties [ 1 , 6 ]. As an example, the resistance of nanocomposites to partial discharges and electric treeing enables the design of new insulation systems with enhanced electrical breakdown strength. Beside electrical properties, mechanical strength as well as thermal conductivity play an important role in selected applications such as insulation systems of large electrical machines. In addition, permittivity and dissipation factor are desired to be as low as possible for electrical insulation whilst for capacitors, loss factor should be as high as possible. Flame retardancy is a property desired for cables insulation used in the radiation field in tunnels, while tracking resistance is very important for outdoor insulators [ 4 ]. The present study highlights the most recent studies and results concerning micro- and nanocomposites materials used in high-voltage applications and possible future work on these materials as the distinctive advantages of polymer based (nano) composites ( i.e. , high temperature performance, improved dielectrics, structural properties and designability) offer promising concepts for the next generation of large motors, generators, transformers and other electrical devices, such as coil forms, slot liners and multifunctional components [7] (see Figure 1). Polymers 2016 , 8 , 173 3 of 62 Figure 1. The next generation of high-voltage applications employing polymer based nanocomposites. 2. From Micro to Nanocomposites in Electrical Engineering In 1987, Ashley described a perspective on advanced materials and the evolution of engineering materials (see Figure 2) [8]. It is obvious that the time scale is non-linear and in 2020, the estimation on materials usage is in a continuous increasing and the rate of change is far faster today than any previous time in history. The rapid rate of change offers opportunities that cannot be ignored by materials scientists, engineers and chemists. As a prominent example, engines efficiency increases at high operating temperatures and this requires high temperature resistant structural materials. However, new materials for rotating machines electrical insulation systems are not only faced by Figure 1. The next generation of high-voltage applications employing polymer based nanocomposites. 3